19/09/18
Page 13 of 67
ASR650 Operational Manual
Antennas out of phase
In this setup the antennas are
‘out of phase’. This is also called anti-parallel- or Anti-Helmholtz
antenna. The optimum tag orientation is 90 degrees rotated compared to those of the single
antenna and
‘double antenna - in phase’ setup.
As you can see in the left drawing, the direction of the field lines varies at different positions. This
makes the anti-parallel setup more suitable for applications with varying transponder orientations
than the other setups.
Nevertheless, this setup has disadvantages as well: There is a dead spot in the middle of the
gate. At this point the tag cannot be read in any orientation. How large this zone is, depends on
antenna size and distance. Please avoid mounting the antennas in positions, where the
animals’
transponder stays in this dead spot. For pure walkthrough applications this fact does not really
matter because the tag should be read without stopping the animal (before and after this spot).
But for applications where animals should be read when they are stopped, e.g. in a scale, it should
be considered carefully.
Additionally, the field is pretty much
‘pushed’ outside the gate – like for magnets with equal
polarity. This extends the reading zone in a way that transponders can be read quite far outside
the panels as well. That could lead to several transponders in the field at the same time and thus
to data collision
– so the reading zone should be checked out doing comprehensive tests before
starting with live animals.
An advantage of the anti-parallel setup is the suppression of far-field interference. This can be an
interesting aspect if long-wave transmitters decrease the reading performance.
Phasing
Phasing